Heat exchanger assembly for air preheater



Sept. 9, 1969 M. R; WHEELER 3,465,815

I HEAT EXCHANGER ASSEMBLY FOR AIR PREHEATER Filed Jan. 5, 1968 2 Sheets-Sheet l Wyn/ma 26 Max 1?. Wink ,4 rramve r p 9, 1969 M. R. WHEELER HEAT EXCHANGER ASSEMBLY FOR AIR IREHEATER Filed Jan. 5, 1968 2 Sheets-Sheet f;

w I f r/bf Am) z by KIM" 4 r A e m Z 2 m lrrmwtk 3,465,815 HEAT EXCHANGER ASSEMBLY FOR AIR PREHEATER Max R. Wheeler, Lynwood, Calif., assignor to Power Replacements, Inc., Costa Mesa, Calif., a corporation of California Filed Jan. 5, 1968, Ser. No. 695,904 Int. Cl. F28d 19/00, 17/00; F23] 15/02 US. Cl. 165-10 2 Claims ABSTRACT OF THE DISCLOSURE Background of the invention Air preheaters of the rotary regenerative type includes a rotor which is mounted for rotation either about a horizontal axis or a vertical axis. The rotor itself is usually made of a plurality of heat transfer elements, which are in the form of heat absorbing corrugated metal plates, and intermediate flat metal plates. The aforesaid heat transfer elements are mounted in 'baskets", and the baskets are then welded together into pie sections, or segments, which, in turn, are formed into a disc-shaped configuration to make up the rotor.

The air preheater described in the preceding paragraph is used, for example, in conjunction with large steamoperated electric generating plants, and the preheater is intended to be operated continually on a twenty-four hour basis. The rotor, carrying the heat transfer elements, causes the elements first to be positioned in the hot gas stream of a gas flue passageway to absorb the heat therefrom, and the elements are then turned by the rotor into an air passageway to impart heat to the incoming air passing therethrough.

Problems have been encountered in the past with the aforementioned air preheaters, especially with the type in which the rotor is mounted for rotation about a horizontal axis. These problems concern the relatively short operational life of the heat transfer elements in the rotor baskets. This short operational life is due, not only to corrosive attack, but also because the elements naturally slide and shift against one another as the rotor turns, thereby creating abrasive wear. Since the rotor rotates normally at two or three revolutions per minute, and in a continuous manner for the life of the heat transfer elements, even a slight relative shifting between the elements creates substantial wear. For example, even as little as .005 inch relative movement between the heat transfer elements becomes significant from a wear standpoint.

It has become usual in the past for the heat transfer elements of the air preheaters under consideration to be composed of flat and corrugated plates or sheets of iron or steel, as mentioned above. These elements have proven to be most susceptible to abrasive wear, as also pointed out. In accordance with recent practices, the aforesaid heat transfer plates have been coated with a porcelain enamel in order to minimize the corrosive attack.

However, the enameled heat transfer elements have been found to be even more susceptible to abrasive wear during the operation of the air preheater in which they are installed. This is because the enameled elements cannot United States Patent be pressed too tightly within the rotor basket, or the enamel will pop off. Since the enameled heat transfer elements are not held within the rotor basket at high compression, they begin to shift as soon as the air preheater mechanism incorporating them is placed into operation, and the abrasive wear begins right from the outset.

The uncoated heat transfer elements can be compressed into the rotor basket with sufficient compression so that an operational life of from 23 years can usually be expected from the rotor, before shifting between the elements and resulting abrasive wear occurs. Thus, in a typical installation using uncoated heat transfer elements, a loss of around 5% in element weight is usually experienced during the first two years. However, the shifting then begins, and during the ensuing six months, the loss in element weight usually jumps to around 20%. Since around 25% of element weight is usually the maximum which can be tolerated, it will be appreciated that very shortly thereafter, replacement of the rotor elements is required.

Therefore, in the horizontal shaft air preheater, the normal operational life of the rotor heat transfer assembly is of the order of two and one-half years. With the enameled type heat transfer element, the life expectancy of the rotor is around six months. Then, as indicated above, expensive replacements are required, in addition to expensive down time of the air preheater itself.

Summary of the invention The improved heat exchanger assembly of the present invention is of the air preheater type which includes a rotor, the rotor being formed of a plurality of baskets, each of which contains a further plurality of heat transfer plates. In the improved construction of the present invention, the heat transfer elements have retaining rods afiixed to them, and these rods are welded or otherwise secured to the holding bars of the rotor baskets. The resulting assembly is one in which mutual abrasive shifting of the heat transfer elements is obviated, and the operational life of the rotor of the air preheater is increased by four or five fold, or more.

Brief description of the drawings FIGURE 1 is a side sectional view of a typical prior art rotary air preheater;

FIGURE 2 is an end view of the rotor used in the air preheater of FIGURE 1, and taken substantially along the line 22 of FIGURE 1;

FIGURE 3 is a perspective view of one of the prior art rotor baskets which may be used in the air preheater shown in FIGURES l and 2;

FIGURE 4 shows a heat transfer element which, in accordance with the concepts of the present invention, includes supporting rods affixed thereto; and

FIGURE 5 shows a rotor basket, constructed in accordance with the concepts of the invention, and including a plurality of heat transfer elements such as shown in FIG- URE 4.

Detailed description of the illustrated embodiment In the drawings, the numeral 10 designates the cylindrical shell of a rotor for a rotary regenerative preheater, which is divided into pie-shaped segments 11 by radial partitions 12 connecting the rotor shell with the rotor shaft 14. The sector shaped compartment is further divided by stay plates into pie-shaped baskets 24, 25 and 26 containing heat transfer elements. These heat transfer elements, as mentioned above, are in the form of corrugated metal sheets which are spaced apart, for example, by interposed fiat metal plates. The heat transfer elements form a series of flow passages parallel to the axis of rotation of the rotor.

In the illustrated embodiment, the rotor is rotatable about a horizontal axis. When the rotor is rotated about its horizontal axis of rotation, the metallic sheets forming the heat transfer elements first absorb heat from the hot gases flowing out of the system and through the flue passageways. Then, as the rotor continues to turn about the horizontal axis, the heated metallic heat transfer elements are moved into a stream of air flowing into the system, so as to heat the air.

As shown in FIGURE 2, the packed plates in the rotor are arranged in their respective baskets according to a predetermined plan, whereby certain of the plates may be arranged substantially parallel to the radially disposed diaphragm, while other plates 22 are arranged substantially perpendicular thereto. However, the air preheater rotor may, if so desired, have all its heat transfer elements extending substantially in the same direction.

In operation, the fluid stream flowing over the mass of corrugated heat transfer elements in the rotor may be used to provide the force required to turn the rotor. Otherwise, the rotor may be turned by a separate motor.

As pointed out above, the heat transfer plates or sheets in the respective baskets of the rotor, in time, become worn and corroded. As also pointed out, a fundamental purpose of the present invention, is to provide a rotor construction, so that the abrasive wear between the elements is reduced to a minimum, so as to prolong the life of the rotor assembly.

FIGURE 3 shows a typical prior art heat exchanger basket, which is welded to other similar baskets, so as to form the rotor shown in FIGURES l and 2. The rotor basket of FIGURE 3 is designated generally as 100. The assembly is formed by bending a three-sided frame 102 into the illustrated configuration, and then by attaching holding bars, such as the illustrated holding bar 104, across each face of the basket. The basket is then filled with heat transfer elements designated 106.

As mentioned above, the aforesaid heat transfer elements may be in the form of corrugated plates, with interposed flat separating plates, so as to define a multiplicity of passageways extending through the basket from one side to the other.

A lid 108 is then placed on the frame 102, and the heat transfer elements 106 are compressed down into the basket, after which the lid 108 is welded or otherwise attached to the frame 102. Further holding bars 110 may be attached to the lid 108 and to the bottom of the frame 102, these latter holding bars also extending across both faces of the basket.

As mentioned above, with a construction such as shown in FIGURE 3, the heat transfer elements 106 may be compressed sufliciently so that the rotor basket will last approximately two or three years before the abrasive shifting between the heat transfer elements becomes a problem, and the resulting wear is such that replacement is necessary.

In the practice of the present invention, each corrugated sheet, such as the corrugated sheet 200 of FIGURE 4 has a pair of retaining rods 202 and 204 extending thereacross, with the retaining rods protruding beyond the two edges of the corrugated sheet heat transfer element 200. Then, as shown in FIGURE 5, the rods 202 and 204 are welded or otherwise attached to the upright holding bars at each side of the basket 100. In this manner, the heat transfer elements, such as the element 200 of FIG- URE 4, are rigidly and securely held within the basket, so that there is no tendency for the adjacent elements to rub against one another with the resulting abrasive wear. By the aforesaid construction, the operational life of the rotor can be extended from a usual '2-3 years up until 10 years or more, before replacement is required.

The invention provides, therefore, an improved heat exchanger rotor basket for an air preheater, or the like. The improved heat exchanger rotor basket of the invention is constructed so that the life of the rotor assembly may be prolonged, so that the frequency at which the rotor elements must be replaced is greatly reduced.

While a particular embodiment of the invention has been shown and described, modifications may be made. It is intended in the following claims to cover all the embodiments which come within the scope of the invention.

What is claimed is:

1. In a rotary regenerative air preheater, and the like, having a rotor adapted to rotate about a particular axis of rotation, said rotor including a plurality of individual baskets each having a peripheral frame defining a front and a back for said basket, and each containing a series of heat-transfer elements which tend to corrode and wear and break after pro-longed usage of the air preheater; the combination of: a plurality of holding bars secured to said frame and respectively extending across said front and back of said basket; and a plurality of rods extending across said heat transfer elements and aflixed to said holding bars to support said heat transfer elements within said frame and to prevent relative movement between said heat transfer elements as said rotor turns.

2. The combination defined in claim 1, in which said heat transfer elements include corrugated metal sheets defining passageways through said basket between said front and said back, and in which said rods are aflixed to respective ones of said sheets.

FOREIGN PATENTS 2/ 1953 Germany.

ROBERT A. OLEARY, Primary Examiner r ALBERT W. DAVIS, Assistant Examiner US. Cl. X.R. -8 

